Ok I think the best option might be to remove the white arrow so it doesn't show behind certain buttons:
.btn, .button, button, .readon, p.readmore a, a.k2ReadMore, .userItemReadMore, div.catItemCommentsLink, .userItemCommentsLink, a.readmore-link, a.comments-link, div.itemCommentsForm form input#submitCommentButton {
background: rgba(0, 0, 0, 0) url("../images/button_arrow.png") no-repeat scroll right center !important;
You can find it located here at template.css line 137
Change it to:
.btn, .button, button, .readon, p.readmore a, a.k2ReadMore, .userItemReadMore, div.catItemCommentsLink, .userItemCommentsLink, a.readmore-link, a.comments-link, div.itemCommentsForm form input#submitCommentButton {
background: rgba(0, 0, 0, 0) !important;
Also the button text color is dark but I believe this is a Jomsocial setting. You should be able to change it to white so it looks better on the blue background of the button.